Our research proposal is to define the role of PRL in lipid metabolism utilizing the unique model of the PRLR-deficient mouse. We will prepare primary cultures of preadipocytes and mature adipocytes at various developmental stages of the mouse. We will compare the rates of growth and differentiation of preadipocytes of PRLR-deficient mice with those of wildtype littermates. We will then examine the effects of PRL and placental lactogen (PL) on the rates of adipocyte differentiation and growth. The differentiation of the preadipocytes will be quantified by measuring the expression of adipogenic transcription factors (C/EBP beta and PPAR gamma) and adipocyte genes and the accumulation of triglyceride. The function of the adipocytes in culture will be assessed by the production/secretion of leptin. We anticipate that the lactogens will increase the rates of differentiation and growth of the preadipocytes in culture and may increase the production of leptin by mature adipocytes. Finally we will compare the effects of the lactogens on BAT growth and differentiation with their effects on WAT development. BAT differentiation and function in PRLR-deficient mice and wildtype littermates will be assessed by analysis of the expression of uncoupling protein-1 under basal conditions and in response to cold and heat stress and by measures of 02 uptake and C02 production using indirect calorimetry. These studies should provide new information regarding the roles of the lactogens in lipid metabolism.